Gas plating with chromium hexacarbonyl



Aug. 3, 1954 P. PAWLYK GAS PLATING WITH CHROMIUM HEXACARBONYL Filed Oct. 8, 1951' briil I. II

M INVENTOR PETER PAWLYK BY Mag ATTORNEYS Patented Aug. 3, 1954 UNITED STATES OFFICE GAS PLATING WITH CHROMIUM HEXACARBONYL Application October 8, 1951, Serial No. 250,304

18 Claims.

where the carbonyl employed has a relatively large proportion of non-metal to metal in the molecule, giving rise to very large volumes of waste gas, it has been considered necessary to operate at low pressures. Thus, for example, it has been customary to operate at pressures in the range of about 0.1 to 0.3 atmospheres where chromium hexacarbonyl is employed, since this compound gives rise to about six volumes of waste gas per molecular weight of metal deposited.

Operation at the low pressures has also been thought to be required in order to secure adherent metallic coats. At the lower pressures the mean free path of the molecules is considerably greater than at atmospheric pressure and the greater velocity attained by the molecules has been believed to be a requirement in the attainment of good bonding between the deposited metal and the base material.

This invention contemplates the provision of a unique process for the deposition of chromium plate from the vapors of chromium hexacarbonyl which process, due to the particular conditions of temperature and gas flow rates employed, is operable at atmospheric pressures.

maintenance of low pressures may be eliminated and the process efiected with relatively simple equipment.

In the practice of the process of invention the chromium hexacarbonyl which vaporizes and decomposes at about 300 F. is maintained in solid form in a carburetor and contacted with an inert carrier gas, as carbon dioxideor nitrogen, at a temperature in the range of about 100 to 290 F. to secure a large vapor pressure of the carbonyl at a temperature below that of decomposition. The mixed vapors of carbonyl and carrier gas are then passed into a chamber, maintained at substantially atmospheric pressure, where the vapors contact the object to be plated and the temperature of which is above that at which decomposition of the carbonyltakesplace, that Thus the usual apparatus necessary for the 2 is, in the range of 550 to 700 F. The flow rate of the gases for successful plating is in the range of l to 3 liters per minute predicated on the flow of carrier gas to the carburetor and at substantially room temperature.

The invention will be more fully understood by reference to the following detailed description, examples, and drawings wherein the single figure illustrates apparatus useful in the process of invention:

Referring to the single figure of the drawing there is shown generally the major'components of the gas plating system at A and B. The letter A indicates the source of plating vapors of controlled temperature, the letter B indicates the plating chamber system.

Referring to source A there is shown at l a tank or cylinder containing liquified carbon dioxide 2 under pressure. A valve 3 on the cylinder is adapted to control the flow of carbon dioxide vapor to conduit 5 through fiow meter 4 secured in the line.

The remote end of conduit 5 is formed into a coil 6 which surrounds a carburetor 1 containing solid chromium hexacarbonyl 8. Coil 6 and carburetor l are immersed in oil 9 contained by tank ill the assembly being heated by an electric heater l2. A thermostatic control having an element l3 immersed in oil 9 is connected by line i l to heater l2 for temperature control of the oil in the known manner. A stirrer l5 operated by motor 56 through suitable belting I1 is used to prevent formation of localized temperature variations in the oil.

An insulated conduit I8 extends from the top of carburetor l and is connected through pump H3 at plating chamber system B at nozzle 20.

Plating chamber system B comprises a chamber 2i having an opening adapted to be closed by cover 22; workpiece 23 is suspended from a support 24 and is positioned between the nozzle 29 and a resistance heating element 25 supported on member 2'6 and electrically connected through connector 27 to a source of power (not shown).

The chamber is substantially surrounded with a water jacket having an inlet 29 and outlet 30. Also provided in a wall of the chamber and passing through the Water jacket is an orifice 3| for the passage of waste gases from the chamber.

A conduit 32 secured in orifice BI is provided with a trap 33 contained in a tank 34 surrounded with cooling water 35 which passes from inlet 36 through outlet 31. A line 38, open to the atmosphere, is provided to conduct away gases not subject to condensation in the trap.

In the process of invention the cleaned metallie workpiece 23 is placed in the chamber and the system is first flushed free of air by passing an inert gas therethrough in any suitable manner.

The valve 3 on cylinder 2 is then opened to permit the passage of approximately 1 liters per minute of carbon dioxide to the coil 6 contained in oil 9, the temperature of which has been raised to and is maintained at about 150 F. The carbon dioxide gas, heated to substantially the same temperature as the oil, then passes into carburetor l.

Carburetor l' and the solid carbonyl contents thereof have also been raised to about the temperature of the oil and consequently a considerable vapor pressure of the carbonyl exists in the chamber. The entering heated carbon dioxide under the influence of the pressures created by the material in tank 2 and the heat absorbed in coil 6, sweep the carbonyl vapors along to pump l9 and chamber 2 I.

The pump 19 may be utilized to supply sufiicient energy tothe-plating gas to overcome losses occurring in line 118 or may serve to provide a definite velocity to the plating gas to achieve a desired result-in the plating chamber.

The gases emanating from nozzle 2t fill chamber .21 and upon striking the workpiece 23, heated by means of elements 25, decompose to deposit metal on'the workpiece. The plate surrounding element 25 may also receive a metallic deposit, but this, is relatively unimportant as the same is heat conductive and recoverable. Substantially no deposition willtake place on the chamber walls as they are cooled below metal decomposition temperature. 1. e. to about 80 Faby the cooling water passing through jacket 28.

The relativelyhigh, that is, substantially atmospheric pressme of the plating gases in chamber .21, when augmented by the pressures of the large volumes of waste gases, creates a flow to orifice .3i, whereaiter any .undecomposed carbonyl platinggas is readily recovered in trap 33.

It may benoted that the-expulsion of the Waste gases is facilitated primarily by the inrush of platin gas and by the cooling effect of the walls remote from the workpiece which .assist in the contraction of gas volume in their immediate .vicinity, creating a pressure gradient towards the opening 9. fromthe point of high pressure-centrallyof the chamber --to the-outlet and the platingaction of the incoming gases is not impeded.

Specific examples ofthe conditionssuitable for plating with chromium hexacarbonyl in the simplified apparatus set forth are given below;

[Flow rate of carrier gas in liters per minute 1 Accordingly the gases move readily 4. Kind of carrier gas CO2 SITime for deposition of .001" of chromium minutes 15 Example II 1. Workpiecetemperatureisteel) F 600 r 2. 'Temperatureof gas at-carburetor F 180 3. Flow rate of carrier gas in liters pe minute 1 4 Kind of-carrier-gas C02 5. Time for depositionbf-flO-l of chromiumm 'minutes 20 4 Example III 1. Workpiece temperature (steel) "F- 700 2. Temperature of gas at carburetor F 280 3. Flow rate of carrier gas in liters per minute 1 4. Kind of carriergasm C02 5. Time for deposition of .001 of chr0- mium minutes 6 Example IV 1. "workpiece temperature (steel) F 550 2. Temperature ofgas at carburetor F Flow rate of carrier gas in liters per minute 3 :4. Kind of carrier gas C02 5. Time for deposition of .001" of chromium "minutes" 60 This example represents threshold conditions for the deposit of chromium.

Example V 1. workpiece temperature (steel) F 700 2. Temperature of'gas at carburetor (carburetor temperature) F 240 3. Flow rate of carrier gas in liters per minute a; 4. Kind of .carrier gas C02 5. Time for deposition of .001" of chromiumminutes 15 The metal upon which the deposition may take place is not a critical'factor as cast iron as -WB11 as steel may be utilized and any metal which will withstand the required "temperature and "bond to the chromium is operable in the process of in Vention.

Other carrier-gases which may be utilized include neon and argon as Well as nitrogen and carbon dioxide.

The particular proportion of chromiumhexacarbonyl present in the platinggas is not critical andmay be varied to suit particular plating requirements and conditions of operation by varying the oil bath'temperature and CO2 flow. The time of plating will however be a function of the hexacarbonyl content and very dilute plating gases will require an excessively long period of operation for a given thickness of-coating. i

This application is related'toco-pending applications Seiial Nos. 250,301; 250,302; 250,303; 250,305; 250,306; and 250,307; all filed October 8, 1951, and all "by the same inventor "as the present application.

It will be understood that'this invention is susceptible of modificationdn"order to adopt it to diilerent usages and conditions andaccordingly it is desired to comprehend such modifications within-this invention as may fall-within the scope of the appended claims.

I claim:

l. A process of plating a metallic objectwith chromium comprising the steps of-heatingthe object to be plated" to a temperature above the decomposition point of gaseous chromium hexacarbonyl, and contacting the heated object/with heat-vaporized "flowing gaseousichromium hexacarbonyl in an atmosphere containing" an inert carrier gas at substantially atmospheric pressures the temperature of thegases and the object being of such a nature that the hexacarbonyl decomposes :to deposit metal on th e' object.

2. A process'of 'p'latin'gfla metallic object' with chromium "comprisingthe steps. of heating the object to be'plated toa ternperaturaabove"the decomposition point or gaseous chromium hexacarbonyl, and contacting the heated object with heat-vaporized flowing gaseous chromium hexacarbonyl in an atmosphere containing an inert carrier gas at substantially atmospheric pressures the temperature'of the gases and the object being such as to cause the hexacarbonyl to decompose and deposit metal on the object.

3. A process of plating a metallic object with chromium comprising the steps of heating the object to be plated to a temperature above the decomposition temperature of chromium hexacarbonyl, and contacting the heated object with heat-vaporized flowing gaseous chromium hexacarbonyl in an atmosphere containing carbon dioxide at substantially atmospheric pressures the temperature of the contacting gases being less than that of the decomposition point of the hexacarbonyl and the temperature of the object and gases and the flow rate being such that decomposition of the gases is caused to deposit metal on the object.

4. A process of plating a metallic object with chromium comprising the steps of heating the object to be plated to a temperature above the decomposition temperature of chromium hexacarbonyl, and contacting the heated object with heat-vaporized flowing gaseous chromium hexacarbonyl in an atmosphere containing nitrogen at substantially atmospheric pressures the temperature of the contacting gases being less than that of the decomposition point of the hexacarbonyl and the temperature of the object and gases and the flow rate being such that decomposition of the gases is caused to deposit metal on the object.

5. A process of plating a metallic object with chromium comprising the steps of heating the object to be plated to a temperature in the range of 550 to 700 F., and contacting the heated object with gaseous chromium hexacarbonyl at a flow rate of about 1-3 liters per minute in an atmosphere containing an inert carrier gas at substantially atmospheric pressure and a temperature range of about 100 to 290 F.

6. A process of plating a metallic object with chromium comprising the steps of heating the object to a temperature of about 600 F., vaporizing the chromium hexacarbonyl at a temperature of about 240 F., contacting the vaporized chromium compound with carbon dioxide gas at a temperature of about 240 F. and at a flow rate of about one liter per minute to form a mixture of the gases, and subjecting the heated object to the action of the flowing gases at substantially atmospheric pressure.

7. A process of plating a metallic object with chromium comprising the steps of heating the object to a temperature of about 600 F., vaporizing the chromium hexacarbonyl at a temperature of about 180 F., contacting the vaporized chromium compound with carbon dioxide gas at a temperature of about 180 F. and ate flow rate of about one liter per minute to form a'mixture of the gases, and subjecting the heated object to the action of the flowing gases at substantially atmospheric pressure.

' 8. A process of plating a metallic object with chromium comprising the steps of heating the object to a temperature of about 700 F., vaporizing the chromium hexacarbonyl at a temperature of about 280 F'., contacting the vaporized chromium compound with carbon dioxide gas at a temperature of about 280 F. and at a flow rate of about one liter per minute to form a mixture of the gases, and subjecting the heated object to the action of the flowing gases at substantially atmospheric pressure.

9. A process of plating a metallic object with chromium comprising the steps of heating the object to a temperature of about 550 F., vaporizing the chromium hexacarbonyl at a temperature of about EL, contacting the vaporized chromium compound with carbon dioxide gas at a temperature or about 100 F. and at a flow rate of about 3 liters per minute to form a mixture'of the gases, and subjecting the heated object to the action of the flowing gases at substantially atmospheric pressure.

10. A process of plating a metallic object with chromium comprising the steps of heating the object to be plated to a temperature of about 550700 F., and contacting the heated object with vaporized hot gaseous chromium hexacarbonyl in an atmosphere of a carrier gas at substantially atmospheric pressure and carrier gas flow rates of one to three liters per minute the temperature of the gases being of such a nature that the hexacarbonyl decomposes to deposit metal upon the object.

11. A process of plating a metallic object with chromium comprising the steps of heating the object to be plated to a temperature of about 550-700 F., and contacting the heated object with vaporized hot gaseous chromium hexaoarbonyl in an atmosphere of a carrier gas at substantially atmospheric pressure and carrier gas flow rates of one to three liters per minute, the temperature of the flowing carrier gas being less than the decomposition temperature of the chromium hexacarbonyl and greater than about 100 F.

12. A process of depositing approximately .001" of chromium on a metallic object comprising the steps of heating the object to be plated to a temperature in the range of about 550 F. to 700 F., and contacting the heated object with a mixture of the gases of chromium hexacarbonyl and carbon dioxide at a temperature in the range of about 100 F. to 290 F. at a flow rate of about one to three liters per minute and substantially atmospheric pressure for a period of about six to sixty minutes.

13. A process of depositing approximately .001" of chromium on a metallic object comprising the steps of heating the object to be plated to a temperature of about 600 F., and contacting the heated object with a mixture of the gases of chromium hexacarbonyl and carbon dioxide at a temperature of about 240 F. at a flow rate of about one liter per minute and substantially atmospheric pressure for a period of about 15 minutes.

14-. A process of depositing approximately .001 of chromium on a metallic object comprising the steps of heating the object to be plated to a temperature of about 600 F., and contacting the heated object with a mixture of the gases of chromium hexacarbonyl and carbon dioxide at a temperature of about 180 F. at a flow rate of about one liter per minute and substantially atmospheric pressure for a period of about 15 minutes.

15. A process of depositing approximately .001" of chromium on a metallic object comprising the steps of heating the object to be plated to a temperature of about 700 F., and contacting the heated object with a mixture of the gases of chromium hexacarbonyl and carbon dioxide at a temperature of about 280 F. at a flow rate of about one liter per minute and. substantially ratmospherig; pressure/ for a; period 1 oi about:;: 15

minutes.

lfiiAvprocess of depositing approximately .001" of chromium on a metallic objectjcomprising the steps of heatingthe. objectito-rbe-plated: to a temperature ofznabout -550iv -an i contacting theeheated object with aimixture of. the -:gases i of chromium :hexacar-bon-yl and carbondioxide at a temperature of about 100 Rataaflomrate; of

about. three liters. per. .-minute and substantially z atmospheric pressure for a I period of. 311361113 915 .minutes.

17. A process of plating a..metallic object with 1chromium..comprising thec steps, of heating the ...object: to: be platedito a temperature. oft-about.

1100? F., vaporizing. the ,chromiumhexacarbonyl at. atemperature of about 240 F.-.; contactingxthe :vaporized chromiumwcompound withcar-bon di- -.0xide. gas at a. flowrate. of about .one literper minute to form amixture ofithe gases,zancl. sub- Wjectingflthe .heated. object to the. action of athe flowing gases at substantially: atmospheric: pressure.

' 18. A process of depositing approximately .001"

.. of chromium on a metallic obj ectcompri i the -steps;of;-heating the objectto a temperature of '.-about:-700 F.; vaporizingwthe .chromium..hexacar- I bonylat artemperatureof about 24051 3.; contactting the :vaporized -chrom-ium compound-with carbon dioxide gasat a fiowvrateof about one .;1iterper-minute to form a-mixture of the gases,

and subjecting thewheatedsobject to the-action of theafiowing-gases for aperiod. of about 15 m-mi-nutes .at, substantially atmospheric pressure.

J. J. Lander and L. H. Garmer, America'mInstiitute: of fMining and MetallurgicalEngineers, Technical Publication #2259, September-1947, 25page 3. 

1. A PROCESS OF PLATING A METALLIC OBJECT WITH CHROMIUM COMPRISING THE STEPS OF HEATING THE OBJECT TO BE PLATED TO A TEMPERATURE ABOVE THE DECOMPOSITION POINT OF GASEOUS CHROMIUM HEXACARBONYL, AND CONTACTING THE HEATED OBJECT WITH HEAT-VAPORIZED FLOWING GASEOUS CHROMIUM HEXA- 